Conventionally, fuel injection nozzles used for gas turbine burners have holes for fuel injection formed penetrating through a cylindrical body wall of a cylindrical member to a hollow section.
A fuel injection nozzle 1 shown in FIG. 6 has nozzle holes 3 that penetrate the wall of a cylindrical body 2 having the shape of a cylinder and through which fluid fuel is injected. The nozzle holes 3 are through-holes formed using a tool, such as a drill, from the outer peripheral side of the cylindrical body 2. When the tool pierces the wall, a machining burr protruding from the inner wall (toward the hollow section) of the cylindrical body 2 is produced. Since the presence of such a machining burr has a negative effect on the flow coefficient (Cd value), it becomes an obstacle to accurate control of the amount of fuel injection. In other words, to enable accurate control of the amount of fuel injection by reducing the variation in the flow coefficient, it is important to eliminate machining burrs (hereinafter, also referred to as “inner burrs”) formed on the inner walls of the nozzle holes 3 to form sharp edges.
Therefore, in the fuel injection nozzle 1 according to the related art, flow control is carried out by forming the nozzle holes 3 through the wall by machining, followed by carrying out a process using, for example, a specialized tool shaped like an earpick having a file formed at the tip to manually remove the inner burr. With such flow control, the prescribed flow coefficient is required to satisfy a predetermined tolerance (for example, within ±10%).
As related art associated with a burr formed at the surface edge of a hole by carrying out drilling on a metal workpiece, a hole forming method and a hole forming drill that serve the dual purpose of removing burrs, which are capable of removing burrs at the same time as forming holes, have been proposed. In that proposal, after forming a hole at a reduced-diameter section at the drill tip, burr removal is carried out by scraping surface burrs with a shoulder portion having an inclined angle of substantially 45 degree with respect to the axial direction of the drill. (For example, refer to Patent Document 1.)
Patent Document 1:
Japanese Unexamined Patent Application, Publication No. HEI-9-239610 (see FIG. 1)